Source : Webster's Revised Unabridged Dictionary (1913)

Apothem \Ap"o*them\, n. [Gr. ? + ? that which is placed, ? to
   place.]
   1. (Math.) The perpendicular from the center to one of the
      sides of a regular polygon.

   2. A deposit formed in a liquid extract of a vegetable
      substance by exposure to the air.